Subcutaneous and intramuscular delivery of liquid drugs by injection is common in the medical arts. As some medications, such as insulin, must be given frequently by injection to an individual, it is desirable that the injections can be performed easily.
Many patients dislike needle injections due to pain or fear for needles. Further, blood-borne pathogens, such as HIV and hepatitis, can be transmitted to health care workers by accidental needle-sticks. Also, the disposal of used needles is a growing concern. This disposal presents a problem to individuals other than healthcare workers. Children, for example, may find used needles in the trash, putting them at risk of contracting infection. Discarded needles likewise pose a risk to waste disposal workers.
In efforts to minimize the fears and risks associated with needle injections, several types of needle-free jet injectors have been developed. These devices penetrate the skin using a high velocity fluid jet, and deliver medication into the tissue of a patient. In order to accomplish this, a force is exerted on the liquid medication. Jet injectors, in general, contain a fluid drug which has been transferred into a chamber having a small orifice at one end. A driver, e.g. a ram, is accelerated using either a coil spring or a compressed gas energy source. The ram impacts a plunger, which in turn creates a high pressure impulse within the chamber. This pressure impulse ejects the fluid medicament through the orifice at high velocity, piercing the skin. The energy source continues to apply a force to the plunger, which quickly propels the drug through the opening in the skin, emptying the syringe in a fraction of a second. The driver may be adapted to provide a two-stage injection, i.e. a first penetrating burst of drug at a high pressure followed by a subsequent delivery of the remaining amount of drug at a lower pressure.
Injectable drugs may be supplied in glass vials sealed with an inert rubber stopper. To administer the fluid drug, the user must transfer the fluid drug from the vial to a fluid drug delivery device, such as a syringe and needle, or a needleless jet injector syringe. Transferring the fluid drug adds cost to administering injections in a hospital or clinic because of the labor expense. Immunizing large populations requires administering many injections per hour, hence transferring the fluid drug presents a significant time constraint. For the patient who must self-administer fluid drugs, such as a diabetic patient requiring several insulin injections a day, transferring the fluid drug can be an inconvenience. Also, with each transfer, there is an opportunity for error in the amount of fluid drug being transferred and administered.
In an effort to eliminate transferring a fluid drug from a vial, pre-filled glass cartridges have been developed. These pre-filled cartridges are similar in design to a syringe. One end is closed and includes either a needle or an inert rubber septum. If a needle is not integral, then a needle subassembly that penetrates the rubber septum is attached prior to use. A movable rubber piston closes the end opposite the needle. To administer the fluid drug, the pre-filled cartridge is placed in a device consisting of a holder and a driver that meets the movable rubber plunger. The user depresses the plunger to dispense the medication.
An example of the use of pre-filled cartridges is in the treatment of diabetes with multiple daily injections of insulin by use of an injection device, e.g. pen-shaped, in which a pre-filled cartridge containing an amount of insulin sufficient for several days can be mounted, the injection device comprising means for setting a desired dose and subsequently expelling the dose. A disadvantage of pre-filled cartridges, however, is that they still require using a needle to penetrate the skin and deliver the medication to the target tissue.
Neither glass vials containing multiple doses of a drug nor pre-filled cartridges can be used with traditional jet injectors. For example, if the force generated by the jet injector drive means was applied directly to the piston the cartridge would in most cases burst. This is because a significant amount of impulse energy is transmitted from the energy source. Although not directly impacted, the glass walls of the cartridge do not have sufficient strength to withstand the large amplitude pressure waves that result when the ram impacts the piston.
Addressing this problem, US patent application 2002/0055707 discloses a jet injection device comprising a reservoir in the form of prefilled drug cartridge, an impulse chamber to which an amount of drug to be expelled by jet action is transferred through a fluid connection between the reservoir and the impulse chamber. The impulse chamber has an injection nozzle at a distal end, and a drive piston adapted to engage a ram member at the proximal end. JP-2001-346878A discloses a similar arrangement in which the drug cartridge is in fluid communication with the impulse chamber through an inlet opening in the impulse piston, fluid communication between the opening and the cartridge being provided by a flexible hose member. U.S. Pat. No. 3,507,276 discloses a jet injector comprising an impulse chamber with a piston, a reservoir being attached to the piston with the piston and reservoir moving as a unit, and WO 2003/105934 discloses an impulse chamber unit with a fixed inlet and a moveable internal piston.
In view of the above, it is an object of the present invention to provide an impulse chamber configuration which allows a cartridge (e.g. conventional) to be used in combination with a jet injection (or nebulizing) device. In the alternative, it is a further object to provide an impulse chamber unit which can be used in combination with a jet injection device adapted to receive a conventional cartridge containing a liquid drug, the impulse chamber unit being simple and compact in design, thus allowing for cost-efficient manufacture, e.g. as a single-use disposable unit.
In the alternative, it is an object to provide an impulse chamber with a nozzle which can be placed against the skin of a subject, the configuration of the impulse chamber allowing for visual inspection of the jet injection site.
In the alternative, it is an object of the invention to provide an impulse chamber and reservoir configuration which allows a small and handy jet injection device to be provided.
In the alternative, it is an object to provide a jet injection device that can be modeled similar in function and form with a conventional pen type injector, to make the patient comfortable with the jet injection device, and so that the jet injection device can easily be utilized by a non-professional user, e.g. a insulin requiring diabetic.